State-insensitive trapping of Rb atoms: linearly versus circularly polarized lights

We study the cancellation of differential ac Stark shifts in the 5s and 5p states of rubidium atom using the linearly and circularly polarized lights by calculating their dynamic polarizabilities. Matrix elements were calculated using a relativistic coupled-cluster method at the single, double and important valence triple excitations approximation including all possible non-linear correlation terms. Some of the important matrix elements were further optimized using the experimental results available for the lifetimes and static polarizabilities of atomic states. "Magic wavelengths" are determined from the differential Stark shifts and results for the linearly polarized light are compared with the previously available results. Possible scope of facilitating state-insensitive optical trapping schemes using the magic wavelengths for circularly polarized light are discussed. Using the optimized matrix elements, the lifetimes of the 4d and 6s states of this atom are ameliorated.Comment: 13 pages, 13 tables and 4 figure

Colossal magnetoresistance in an ultra-clean weakly interacting 2D Fermi liquid

We report the observation of a new phenomenon of colossal magnetoresistance in a 40 nm wide GaAs quantum well in the presence of an external magnetic field applied parallel to the high-mobility 2D electron layer. In a strong magnetic field, the magnetoresistance is observed to increase by a factor of ~300 from 0 to 45T without the system undergoing any metal-insulator transition. We discuss how this colossal magnetoresistance effect cannot be attributed to the spin degree-of-freedom or localization physics, but most likely emanates from strong magneto-orbital coupling between the two-dimensional electron gas and the magnetic field. Our observation is consistent with a field-induced 2D-to-3D transition in the confined electronic system

Generalized Stueckelberg-Higgs gauge theories

The aim of this work is to discuss and explorer some generalized aspects of generation of photon mass respecting gauge symmetry. So with this intention we introduce the generalized Stueckelberg and Higgs gauge theories and present the classical and quantum conceptual aspects. We construct the quantum theory by writing the transition amplitude in the Fadeev-Senjanovic formalism and put it in a covariant form by the Fadeev-Popov method. Posteriorly we analyze the independence of physics by gauge choices via BRST symmetry. As we will see, the Stueckelberg structure has influence in the quantization process of the Higgs theory in the Gerardus 't Hooft shape, in which we see an intimate relationship between the Stueckelberg compensating field and the Goldstone boson. The degrees of freedom are explored not only in the quantization process, due to the constraints in gauge theories, but also in the Goldstone theorem, wherein we understand how the generalized gauge field eat the Goldstone boson and acquire mass